Hair analysis method

A method for the direct analysis of the presence of an analyte which becomes embedded in keratinized structures, e.g., hair, fingernails and toenails, from the bloodstream of a subject which comprises preparing a mixture containing dithiothreitol or dithioerythritol (“DTT”), an enzyme suitable for the digestion of the keratin structure and a sample of the keratin structure; permitting the enzyme to digest the sample of keratin structure to form a digest solution, followed by the addition of a salt of a metal of copper, zinc, manganese, iron, lead, cadmium, mercury, silver and cobalt to deactivate the DTT; and finally subjecting the digest solution to analysis to determine the presence of the analyte in the keratin structure sample. The protease enzymes papain, chymopapain, and proteinase K are preferred for use in the invention.